There will always be disagreements on some religious, cultural, and social issues among the members of a diverse group. This is the main function of social customs to deal with all these differences of opinion. because you have not introduced the "it" or "that" the only way to rewrite the sentence is to make it a statement. "there will always be disagreements [ --------- ]. This is the [ -- -- -------]."

Hi. Firstly, I would dispense with the always, in the phrase ‘it always seems probable’. Secondly, I would start the second sentence with a statement: the main function of ... By starting the sentence with the word ‘this’ you are implying that you have introduced the idea in the previous sentence. When you use pronouns, or words like this and that, be sure to ask yourself what you are referring to. Not making this clear is a common fault in the academic writing of even English first language speakers :)

In proper writing, “this” and “that” need to introduce nouns and not whole ideas. I would rewrite the second sentence like so: This conflict (These disagreements) is the main focus of social customs, to deal with all these differences of opinion. I also added the comma because the second part of the sentence reads more like an aside (or side comment) which we set out with commas. Hope that helps!